The role of protein phosphatases in the regulation of mitogen and stress-activated protein kinases.

It is now established that a family of dual-specificity protein phosphatases are able to interact with mitogen and stress-activated protein kinases in a highly specific manner to differentially regulate these enzymes in mammalian cells. A role for these proteins in negative feedback regulation of MAP kinase activity is also supported by genetic and biochemical studies in yeasts and Drosophila. More recently it has become clear that other classes of protein phosphatase also play key roles in the regulated dephosphorylation of MAP kinases, including tyrosine-specific protein phosphatases and serine/threonine protein phosphatases. It is likely that a complex balance between upstream activators and these different classes of MAP kinase specific phosphatase are responsible for determining, at least in part, the magnitude and duration of MAP kinase activation and hence the physiological outcome of signalling.